Hybrid brake systems and methods for load cell calibration

ABSTRACT

A braking system for an aircraft may comprise: a brake assembly; a hydraulic braking subsystem having a hydraulic brake actuator configured to operate the brake assembly; an electric braking subsystem having an electric brake actuator configured to operate the brake assembly and a load cell configured to measure a force supplied by the electric brake actuator; a hydraulic brake control unit configured to control the hydraulic braking subsystem; and an electric brake control unit configured to control the electric braking subsystem, the electric brake control unit in operable communication with the hydraulic brake control unit, the electric brake control unit configured to calibrate the load cell by a scale factor based on a measured force from the load cell, a measured hydraulic pressure used to exceed the measured force received from the hydraulic brake control unit, and a piston area of the hydraulic brake actuator.

FIELD

The present disclosure relates to aircraft wheel and brake systems and,more particularly, to systems and methods for load cell driftcompensation and health prognostics.

BACKGROUND

Aircraft typically utilize brake systems on wheels to slow or stop theaircraft during landings, taxiing and emergency situations, such as, forexample, a rejected take off (RTO). The brake systems generally employ aheat sink comprising a series of friction disks, disposed between apressure plate and an end plate, that may be forced into sliding contactwith one another during a brake application to slow or stop theaircraft.

A typical hydraulic brake system may include, without limitation, asource of pressurized hydraulic fluid, a hydraulic actuator for exertinga force across the heat sink (e.g., across the pressure plate, theseries of friction disks and the end plate), a valve for controlling apressure level provided to the hydraulic actuator and a brake controlunit for receiving inputs from a pilot and from various feedbackmechanisms and for producing responsive outputs to the valve. Uponactivation of the brake system (e.g., by depressing a brake pedal), apressurized fluid is applied to the hydraulic actuator, which maycomprise a piston configured to translate the pressure plate toward theend plate. A typical electric brake system includes variouselectromechanical counterparts to a hydraulic brake system, such as, forexample, an electromechanical brake actuator (EBA) in place of thehydraulic actuator and a source of electric power in place of the sourceof pressurized hydraulic fluid. Load cells used in EBAs can be prone todrift over time due to various external factors such as vibration forexample.

SUMMARY

A braking system for an aircraft is disclosed herein. The braking systemmay comprise: a brake assembly; a hydraulic braking subsystem having ahydraulic brake actuator configured to operate the brake assembly; anelectric braking subsystem having an electric brake actuator configuredto operate the brake assembly and a load cell configured to measure aforce supplied by the electric brake actuator; a hydraulic brake controlunit configured to control the hydraulic braking subsystem; and anelectric brake control unit configured to control the electric brakingsubsystem, the electric brake control unit in operable communicationwith the hydraulic brake control unit, the electric brake control unitconfigured to calibrate the load cell by a scale factor based on ameasured force from the load cell, a measured hydraulic pressure used toexceed the measured force received from the hydraulic brake controlunit, and a piston area of the hydraulic brake actuator.

In various embodiments, the electric brake control unit is furtherconfigured to store any scale factors that exceed a scale factorthreshold as the scale factor threshold. The electric brake control unitmay be further configured to count a number of times the scale factorthreshold is applied to a force measurement of the load cell. Theelectric brake control unit may be further configured to generate anotification in response to the number of times exceeding a countthreshold.

In various embodiments, the electric brake control unit is furtherconfigured to command the electric brake actuator to supply a firstforce to a brake stack of the brake assembly; and the hydraulic brakecontrol unit is further configured to command the hydraulic brakingsubsystem to increase a supplied pressure to the brake stack via thehydraulic brake actuator at a predetermined rate to determine thehydraulic pressure used to exceed the measured force.

In various embodiments, the electric brake control unit is furtherconfigured to determine the hydraulic pressure from used to exceed themeasured force based on the measured force dropping from an initialmeasured force and pressure data received from the hydraulic brakecontrol unit.

In various embodiments, the electric brake control unit is furtherconfigured to determine a set of scale factors including the scalefactor, each scale factor in the set of scale factors associated with acommanded force for the electric brake actuator. A scale factor may beinterpolated in response to a second commanded force being between afirst commanded force having a first scale factor and the secondcommanded force having a second scale factor. The electric brake controlunit may be further configured to monitor a health of the load cell.

In various embodiments, the electric brake control unit is configured tocalibrate the load cell at a predetermined time interval.

An article of manufacture is disclosed herein. The article ofmanufacture may include a tangible, non-transitory computer-readablestorage medium having instructions stored thereon that, in response toexecution by a processor, cause the processor to perform operationscomprising: commanding, via the processor, an electric brake actuator ofan electric braking subsystem of a braking system to supply a firstforce to a brake stack in the braking system; receiving, via theprocessor and from a hydraulic brake control unit, a pressure datacorresponding to a supplied pressure to the brake stack via a hydraulicbrake actuator at a predetermined rate; determining, via the processorand based on the pressure data, a pressure that causes a forcemeasurement of a load cell of the electric braking subsystem of thebraking system to drop; and calibrating, via the processor, the loadcell based on the pressure, the force measurement, and a piston contactarea of the electric brake actuator.

In various embodiments, the operations further comprise calculating aforce based on the pressure and the piston contact area prior tocalibrating.

In various embodiments, calibrating the load cell comprises determininga scale factor for force measurement of the load cell that correlatedwith a commanded force of the electric brake actuator. The operationsmay further comprise determining a set of scale factors, each scalefactor in the set of scale factors associated with the commanded forceof the electric brake actuator. The set of scale factors may beassociated with a ratio of the commanded force to a max rated forcewithin a range of ratios. The range of ratios may be between 10% and 90%of the max rated force for the electric brake actuator.

An article of manufacture is disclosed herein. The article ofmanufacture may include a tangible, non-transitory computer-readablestorage medium having instructions stored thereon that, in response toexecution by a processor, cause the processor to perform operationscomprising: determining, via the processor, a set of scale factors for aload cell of an electric braking subsystem of a braking system, eachscale factor in the set of scale factors associated with a commandedforce of an electric brake actuator; storing any scale factors thatexceed a scale factor threshold as being the scale factor threshold;counting a number of times the load cell is scaled using the scalefactor threshold as the scale factor; and generating a notification inresponse to the number of times exceeding a count threshold.

In various embodiments, the operations further comprise re-calibrating,via the processor, the load cell of the electric braking subsystem. Theoperations may further comprise re-setting, via the processor, thecounting to zero in response to the scale factor that exceeded the scalefactor threshold dropping below the scale factor threshold.

In various embodiments, determining the set of scale factors comprisescalculating a scale factor for a measured force of the load cell at thecommanded force of the electric brake actuator to a brake stack based ona supplied hydraulic pressure that forces a hydraulic brake actuator toreduce the measured force on the brake stack.

The foregoing features and elements may be combined in any combination,without exclusivity, unless expressly indicated herein otherwise. Thesefeatures and elements as well as the operation of the disclosedembodiments will become more apparent in light of the followingdescription and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the following detailed description andclaims in connection with the following drawings. While the drawingsillustrate various embodiments employing the principles describedherein, the drawings do not limit the scope of the claims.

FIG. 1A illustrates an aircraft having multiple landing gear and brakes,in accordance with various embodiments;

FIG. 1B is a block diagram of a brake control unit, in accordance withvarious embodiments;

FIG. 1C is a schematic diagram of a brake assembly, in accordance withvarious embodiments; and

FIGS. 2A and 2B are functional diagrams of a hybrid or redundant brakingsystem, in accordance with various embodiments

FIG. 3 illustrates a process for load cell calibration, in accordancewith various embodiments; and

FIG. 4 illustrates a process for health management of an electric brakeactuator, in accordance with various embodiments.

DETAILED DESCRIPTION

The following detailed description of various embodiments herein makesreference to the accompanying drawings, which show various embodimentsby way of illustration. While these various embodiments are described insufficient detail to enable those skilled in the art to practice thedisclosure, it should be understood that other embodiments may berealized and that changes may be made without departing from the scopeof the disclosure. Thus, the detailed description herein is presentedfor purposes of illustration only and not of limitation. Furthermore,any reference to singular includes plural embodiments, and any referenceto more than one component or step may include a singular embodiment orstep. Also, any reference to attached, fixed, connected, or the like mayinclude permanent, removable, temporary, partial, full or any otherpossible attachment option. Additionally, any reference to withoutcontact (or similar phrases) may also include reduced contact or minimalcontact. It should also be understood that unless specifically statedotherwise, references to “a,” “an” or “the” may include one or more thanone and that reference to an item in the singular may also include theitem in the plural. Further, all ranges may include upper and lowervalues and all ranges and ratio limits disclosed herein may be combined.

Referring now to FIG. 1A, an aircraft 100 includes multiple landing gearsystems, including a first landing gear 102 (or a port-side landinggear), a second landing gear 104 (or a nose landing gear) and a thirdlanding gear 106 (or a starboard-side landing gear). The first landinggear 102, the second landing gear 104 and the third landing gear 106each include one or more wheel assemblies. For example, the thirdlanding gear 106 includes an inner wheel assembly 108 and an outer wheelassembly 110. The first landing gear 102, the second landing gear 104and the third landing gear 106 support the aircraft 100 when theaircraft 100 is not flying, thereby enabling the aircraft 100 to takeoff, land and taxi without incurring damage. In various embodiments, oneor more of the first landing gear 102, the second landing gear 104 andthe third landing gear 106 is operationally retractable into theaircraft 100 while the aircraft 100 is in flight.

In various embodiments, the aircraft 100 further includes an avionicsunit 112, which includes one or more controllers (e.g., processors) andone or more tangible, non-transitory memories capable of implementingdigital or programmatic logic. In various embodiments, for example, theone or more controllers are one or more of a general purpose processor,digital signal processor (DSP), application specific integrated circuit(ASIC), field programmable gate array (FPGA) or other programmable logicdevice, discrete gate, transistor logic, or discrete hardware component,or any of various combinations thereof or the like. In variousembodiments, the avionics unit 112 controls operation of variouscomponents of the aircraft 100. For example, the avionics unit 112controls various parameters of flight, such as an air traffic managementsystems, auto-pilot systems, auto-thrust systems, crew alerting systems,electrical systems, electronic checklist systems, electronic flight bagsystems, engine systems flight control systems, environmental systems,hydraulics systems, lighting systems, pneumatics systems, trafficavoidance systems, trim systems, brake systems and the like.

In various embodiments, the aircraft 100 further includes brake controlunits (BCUs) 120 (e.g., hydraulic brake control unit 220 and electricbrake control unit 250 as described further herein). With briefreference now to FIG. 1B, the BCUs 120 include one or more controllers115 (e.g., processors) and one or more memories 116 (e.g., tangible,non-transitory memories) capable of implementing digital or programablelogic. In various embodiments, for example, the one or more controllers115 is one or more of a general purpose processor, DSP, ASIC, FPGA, orother programmable logic device, discrete gate, transistor logic, ordiscrete hardware component, or any of various combinations thereof orthe like, and the one or more memories 116 is configured to storeinstructions that are implemented by the one or more controllers 115 forperforming various functions, such as adjusting the hydraulic pressureor electric power provided to a brake actuator depending on the degreeof braking desired. In various embodiments, the BCUs 120 control thebraking of the aircraft 100. For example, the BCUs 120 control variousparameters of braking, such as manual brake control, automatic brakecontrol, antiskid braking, locked wheel protection, touchdownprotection, emergency/parking brake monitoring or gear retractionbraking. The BCUs 120 may further include hardware 117 capable ofperforming various logic using discrete power signals received fromvarious aircraft systems. Referring again to FIG. 1A, the aircraft 100further includes one or more brake assemblies coupled to each wheelassembly. For example, a brake assembly 118 is coupled to the outerwheel assembly 110 of the third landing gear 106 of the aircraft 100.During operation, the brake assembly 118 applies a braking force to theouter wheel assembly 110 upon receiving a brake command from the BCUs120. In various embodiments, the outer wheel assembly 110 of the thirdlanding gear 106 of the aircraft 100 (or of any of the other landinggear described above and herein) comprises any number of wheels or brakeassemblies.

Referring now to FIG. 1C, schematic details of the brake assembly 118illustrated in FIG. 1A are provided. In various embodiments, the brakeassembly 118 is mounted on an axle 130 for use with a wheel 132 disposedon and configured to rotate about the axle 130 via one or more bearingassemblies 134. A central axis 136 extends through the axle 130 anddefines a center of rotation of the wheel 132. A torque plate barrel 138(sometimes referred to as a torque tube or barrel or a torque plate) isaligned concentrically with the central axis 136, and the wheel 132 isrotatable relative to the torque plate barrel 138. The brake assembly118 includes an actuator ram assembly 140, a pressure plate 142 disposedadjacent the actuator ram assembly 140, an end plate 144 positioned adistal location from the actuator ram assembly 140, and a plurality ofrotor disks 146 interleaved with a plurality of stator disks 148positioned intermediate the pressure plate 142 and the end plate 144.The pressure plate 142, the plurality of rotor disks 146, the pluralityof stator disks 148 and the end plate 144 together form a brake heatsink or brake stack 150. The pressure plate 142, the end plate 144 andthe plurality of stator disks 148 are mounted to the torque plate barrel138 and remain rotationally stationary relative to the axle 130. Theplurality of rotor disks 146 is mounted to the wheel 132 and rotate withrespect to each of the pressure plate 142, the end plate 144 and theplurality of stator disks 148.

An actuating mechanism for the brake assembly 118 includes a pluralityof actuator ram assemblies, including the actuator ram assembly 140,circumferentially spaced around a piston housing 152 (only one actuatorram assembly is illustrated in FIG. 1C). Upon actuation, the pluralityof actuator ram assemblies affects a braking action by urging thepressure plate 142 and the plurality of stator disks 148 into frictionalengagement with the plurality of rotor disks 146 and against the endplate 144. Through compression of the plurality of rotor disks 146 andthe plurality of stator disks 148 between the pressure plate 142 and theend plate 144, the resulting frictional contact slows or stops orotherwise prevents rotation of the wheel 132. In various embodiments,the plurality of rotor disks 146 and the plurality of stator disks 148are fabricated from various materials, such as, for example, ceramicmatrix composite materials, that enable the brake disks to withstand anddissipate the heat generated during and following a braking action. Asdiscussed in further detail below, in various embodiments, the actuatorram assemblies comprise a combination of electrically operated actuatorrams (or electric brake actuators) and hydraulically operated (orpneumatically operated) actuator rams (or hydraulic brake actuators orpneumatic brake actuators).

Referring now to FIG. 2A, a braking system 200 (or a redundant brakingsystem or a hybrid braking system) is illustrated, in accordance withvarious embodiments. Generally, the braking system 200 may be separatedinto a hydraulic braking subsystem 202 and an electric braking subsystem204. Referring first to the hydraulic braking subsystem 202, the brakingsystem 200 includes a hydraulic brake control unit 220, which isprogrammed to control the various braking functions performed by thehydraulic braking subsystem 202. The hydraulic braking subsystem 202includes a hydraulic power source 222 configured to provide a hydraulicfluid to a primary brake control module 224 via a primary hydraulic line226. A primary pressure transducer 228 senses the pressure of thehydraulic fluid and provides a signal reflective of the pressure to thehydraulic brake control unit 220 via a data circuit 230. In variousembodiments, the hydraulic braking subsystem 202 includes a hydraulicfluid return 232 that is configured to return hydraulic fluid from theprimary brake control module 224 to the hydraulic power source 222 via areturn hydraulic line 234. In various embodiments, the hydraulic powersource 222 comprises a valve (e.g., a solenoid valve) configured tocontrol a hydraulic pressure supplied to the hydraulic brake actuator217, in accordance with various embodiments.

A secondary hydraulic line 236 fluidly couples the primary brake controlmodule 224 to a brake assembly 218, similar to the brake assembly 118described above with reference to FIG. 1A. More particularly, thesecondary hydraulic line 236 is fluidly coupled to a hydraulic brakeactuator 217 (or a plurality of hydraulic brake actuators) housed withinthe brake assembly 218. In various embodiments, a fuse 238 is fluidlycoupled to the secondary hydraulic line 236 downstream of the primarybrake control module 224. The fuse 238 acts as a shut-off valve orswitch in the event the secondary hydraulic line 236 experiences a lossof pressure—e.g., in the event of a leak in the secondary hydraulic line236 or the brake assembly 218—thereby preventing hydraulic fluid fromcontinuing to flow to the secondary hydraulic line 236 and leaking outof the hydraulic system. A secondary pressure transducer 240 is fluidlycoupled to the secondary hydraulic line 236 and electrically coupled tothe hydraulic brake control unit 220 via the data circuit 230. In theevent the secondary pressure transducer 240 senses a loss of pressurewithin the secondary hydraulic line 236, the hydraulic brake controlunit 220 may, in redundant fashion, pass control of the braking system200 to the electric braking subsystem 204. As illustrated, the secondaryhydraulic line 236, the fuse 238, the secondary pressure transducer 240and the brake assembly 218 are replicated for each of a plurality ofouter wheel assemblies 210 and for each of a plurality of inner wheelassemblies 211 comprised within the braking system 200. Without loss ofgenerality, in various embodiments, the hydraulic braking subsystem 202also includes wheel speed transducers and brake temperature sensors,such as, for example, an inboard wheel speed transducer 242 and anoutboard wheel speed transducer 243, and an inboard brake temperaturesensor 244 and an outboard brake temperature sensor 245.

Referring now to the electric braking subsystem 204, the braking system200 includes an electric brake control unit 250, which is programmed tocontrol the various braking functions performed by the electric brakingsubsystem 204. The electric braking subsystem 204 includes an electricpower source 252 configured to provide electric power to an electricbrake actuator controller 254, which, for example, may be an inboardelectric brake actuator controller or an outboard electric brakeactuator controller. The electric power is provided to the electricbrake actuator controller 254 via an electric power circuit 257. Theelectric brake actuator controller 254 is electrically coupled to anelectric brake actuator 219 (or a plurality of electric brake actuators)that is housed within the brake assembly 218. In various embodiments,the electric brake control unit 250 provides force commands to theelectric brake actuator controller 254, which in turn provides a currentcommand to the electric brake actuator 219 to apply force, directing theelectric brake actuator 219 to cause the brake assembly 218 tomechanically operate, thereby driving the brake assembly 218 to providebraking power. In various embodiments, the electric brake actuatorcontroller 254 monitors the load cell 259 (e.g., via the controlcircuitry 256) to apply more or less current to achieve a desired force.In various embodiments, the electric brake actuator controller 254 iscoupled to the electric brake control unit 250 via a communication link258. The communication link 258 may comprise, for example, a controllerarea network bus 260. Similar to the hydraulic braking subsystem 202,and without loss of generality, the electric braking subsystem 204 alsoincludes wheel speed transducers, such as, for example, an inboard wheelspeed transducer 262 and an outboard wheel speed transducer 263, orbrake temperature sensors.

In various embodiments, the electric brake actuator controller 254 iscoupled to the electric brake control unit 250 via a communication link258. The communication link 258 may comprise, for example, a controllerarea network bus 260. Similar to the hydraulic braking subsystem 202,and without loss of generality, the electric braking subsystem 204 alsoincludes wheel speed transducers, such as, for example, an inboard wheelspeed transducer 262 and an outboard wheel speed transducer 263, orbrake temperature sensors.

In various embodiments, the load cell 259 for each electric brakeactuator 219 in the electric braking subsystem 204 may be prone to driftover time (i.e., when a measured force by the load cell 259 fluctuates,leading to inaccurate measurements). In this regard, calibrating theload cell 259 may provide a manner of monitoring a load cell health,determining a servicing time for the load cell 259, or the like. Invarious embodiments, the hydraulic braking subsystem 202 may facilitatecalibration of the load cell 259 as described further herein.

In various embodiments the load cell 259 for each electric brakeactuator 219 in the electric braking subsystem 204 measures a forceapplied to the brake stack 150 from FIG. 1C at the electric brakeactuator 219 location. In various embodiments, the load cell 259 may becalibrated based on comparing the force measured to a hydraulic pressureas described further herein.

Referring now to FIG. 2B, the brake assembly 218 is described withfurther detail. As illustrated, the brake assembly 218 includes apressure plate 215 configured to apply a compressive load against abrake stack or heat sink, which includes a plurality of brake rotors anda plurality of brake stators disposed between the pressure plate and anend plate. As described above, the brake assembly 218 includes thehydraulic brake actuator 217 (or a plurality of such hydraulic brakeactuators) and the electric brake actuator 219 (or a plurality of suchelectric brake actuators). In various embodiments, the brake assembly218 includes four electric brake actuators spaced at ninety degree (90°)intervals about the pressure plate 215 and four hydraulic brakeactuators spaced at ninety degree (90°) intervals about the pressureplate 215, with each electric brake actuator and each hydraulic brakeactuator spaced at forty-five degree (45°) intervals. Fewer or greaternumbers of actuators, both electric and hydraulic, are contemplatedwithin the scope of the disclosure.

Referring back to FIG. 2A, during operation, a pilot or a co-pilotdepresses a pilot brake pedal 270 or a co-pilot brake pedal 272, each ofwhich is connected to a hydraulic brake position sensor 274 and to anelectric brake position sensor 276. The hydraulic brake position sensor274 generates a signal reflective of the pedal position that istransmitted to the hydraulic brake control unit 220 via a hydraulicbrake sensor bus 278. The hydraulic brake control unit 220, if employed,then activates the hydraulic brake actuator 217 based on a currentsignal that is transmitted to the primary brake control module 224 via aprimary brake control bus 225. Similarly, the electric brake positionsensor 276 generates a signal reflective of the pedal position that istransmitted to the electric brake control unit 250 via an electric brakesensor bus 280. The electric brake control unit 250, if employed, thenactivates the electric brake actuator 219 based on a force request thatis transmitted to the electric brake actuator controller 254 via thecommunication link 258. In various embodiments, an avionics system 282is configured to employ one or both of the hydraulic braking subsystem202 and the electric braking subsystem 204 via signals transmitted overa respective data bus 283. In various embodiments, an autobrake selector284 is configured to employ one or both of the hydraulic brakingsubsystem 202 and the electric braking subsystem 204 via signalstransmitted over an autobrake data bus 285.

The braking system 200 may operate in a fully hydraulic mode, employingonly the hydraulic braking subsystem 202, or in a fully electric mode,employing only the electric braking subsystem 204. In addition, thedisclosure contemplates, in various embodiments, the hydraulic brakingsubsystem 202 being employed as the principal braking system, while theelectric braking subsystem 204 is employed as a backup braking system inthe event a failure occurs with the hydraulic braking subsystem 202. Thedisclosure also contemplates, in various embodiments, the electricbraking subsystem 204 being employed as a parking brake when theaircraft is at rest. In various embodiments, the hydraulic brake controlunit 220 and the electric brake control unit 250 are configured tocommunicate with one another via an intercommunication bus 286. Suchcommunication enables, for example, transfer of control from thehydraulic brake control unit 220 to the electric brake control unit 250following a failure of the hydraulic braking subsystem 202. For example,in the event the hydraulic brake control unit 220 detects a leak ofhydraulic fluid within the hydraulic braking subsystem 202, thehydraulic brake control unit 220 may communicate with the electric brakecontrol unit 250 and transfer control of the braking system 200 to theelectric brake control unit 250. Similarly, in the event the electricbrake control unit 250 detects a failure within the electric brakingsubsystem 204, the electric brake control unit 250 may communicate withthe hydraulic brake control unit 220 and transfer control of the brakingsystem 200 to the hydraulic brake control unit 220. In this regard, aprimary braking system and a secondary braking system may be determinedfor each flight cycle as described further herein. Based on a failure tothe primary braking system being detected, the BCUs 120 are configuredto transfer control from the primary braking system to the secondarybraking system.

The above disclosure provides for a hybrid braking architecture. Invarious embodiments, the architecture employs hydraulic power for normalbraking and electric power for an alternate braking system or a parkingbrake system. The architecture provides a fully redundant braking systemfor normal pedal operated braking and for emergency braking. In variousembodiments, the piston housing (e.g., the piston housing 152 referredto in FIG. 1C) is modified to accept four hydraulic actuators and fourelectric actuators, spaced equally and alternating between one hydraulicactuator and one electric actuator; though any number of actuators iscontemplated by the disclosure. The equal spacing of forty-five degrees(45°) between alternating hydraulic and electric brake actuators allowsfor uniform force application on the brake stack when the hydraulicsystem is active or the electric system is active.

In various embodiments, the architecture is operated using pedals in thecockpit. This allows seamless activity and minimum pilot effort when,for example, the emergency system is engaged. The architecture istransparent for actuation (e.g., automated), although crew-alertingsystem (CAS) messages may be employed to inform the pilot that theemergency system (e.g., the electric braking subsystem) has becomeactive. The hydraulic and electric brake control units are in constantcommunication using, for example, controller area network (CAN)communication links, such that when the primary brake control unit(either the hydraulic or the electric brake control unit) detects a lossof braking or other fault, the alternate brake control unit (either thehydraulic or the electric brake control unit) may take over control andoperate the braking. In various embodiments, a switch may also beprovided in the cockpit to allow the pilot to manually switch from theone braking subsystem to the other—e.g., the hydraulic subsystem to theelectric sub system—depending on the failure and any other issues orfaults occurring with the power supplies or other aircraft systemdegradations.

Referring now to FIG. 3 , a process 300 for calibrating a load cell 259of an electric brake actuator 219 of the braking system 200 isillustrated, in accordance with various embodiments. The process 300 maybe performed by the BCUs 120 (e.g., the electric brake control unit 250and the hydraulic brake control unit 220), in accordance with variousembodiments.

The process 300 comprises determining aircraft conditions are acceptablefor calibration (step 302). For example, the BCUs 120 (e.g., theelectric brake control unit 250 and the hydraulic brake control unit220) may determine that a parking brake is enabled, there are weight onwheels, and the BCUs 120 have just been powered on. In this regard, theBCUs 120 may determine that the aircraft conditions are acceptable forperforming the calibration process 300. The calibration process 300 maybe performed at any predetermined interval (e.g., every 10 flightcycles, every 100 flight cycles, or the like). The present disclosure isnot limited in this regard.

The process 300 further comprises commanding the electric brake actuator219 to supply a first force to a brake stack 150 (step 304). In variousembodiment, the first force may be based on a percentage of a max ratedforce for the electric brake actuator (e.g., 10%, 20%, 30%, etc.).

The process 300 further comprises receiving a force measurement from aload cell 259 in response to the first force being supplied to the brakestack 150 (step 306). The first force may provide feedback to theelectric brake control unit 250 that the first force is around thepercentage of the max rated force the electric brake actuator 219 wascommanded to supply.

The process 300 further comprises commanding a hydraulic brake actuator217 to increase a supplied pressure to the brake stack at apredetermined rate (step 308). In this regard, the hydraulic brakepressure supplied to the brake stack 150 may be steadily increased fromzero at the predetermined rate (e.g., 20 psi/s (138 kPa/s). Thus, thehydraulic brake actuator 217 may be supplying a pressure simultaneouslywith the electric brake actuator supplying the first force. In variousembodiments, the hydraulic brake control unit 220 is configured toprovide pressure data (e.g., received from primary pressure transducer228) to the electric brake control unit 250 during the process 300.

The process 300 further comprises determining a pressure that causes theforce measurement to drop (step 310). Once the force measurement beingreceived in step 306 begins to drop, the force supplied by the pistondue to the hydraulic brake pressure of the hydraulic brake actuator 217will have exceeded the first force supplied by the electric brakeactuator 219.

In this regard, based on the pressure determined from step 310 andcontact area of a piston of the hydraulic brake actuator 217, a forcethat caused the force measurement provided by the load cell to drop iscalculated (step 312). In this regard, the force supplied by the pistondue to the hydraulic pressure of the hydraulic brake actuator may becompared to the force measurement from the load cell 259.

Based on the force and the force measurement, the load cell 259 may becalibrated (step 314). In various embodiments, steps 304-312 may berepeated for various first forces in step 304 (e.g., 10% of max ratedforce, 20% of max rated force, 30% of max rated force, etc.).

In various embodiments, the calibration step (e.g., step 312) maydetermine a scaling factor to be applied to force measurements of theload cell 259 based on the process 300. For example, if the load cellmeasurement of the load cell 259 is within a predetermined tolerance(e.g., +/−50 lbs (22.7 kg)), the electric brake control unit 250 maydetermine that no scaling is to be performed for future forcemeasurements of the load cell 259. In various embodiments, if the loadcell measurements of the load cell 259 are outside of the predeterminedtolerance, the electric brake control unit 250 may calculate a scalefactor that would scale the force measurement of the load cell 259 tothe force calculated from step 312. In various embodiments, the scalefactor may be associated with a specific force (e.g., 10% of a max ratedforce has a first scale factor, 20% of max rated force has a secondscale factor, etc.). In various embodiments, a single scale factor maybe calculated based on averaging a calculated scale factor at variousforces between 10% and 90% of a max rated force for the electric brakeactuator 219. The present disclosure is not limited in this regard. Invarious embodiments, when each rated force has an associated scalefactor, the electric brake control unit 250 may interpolate a scalefactor in response to receiving a force measurement between two forcedata points from process 300, or use the closest scaling factorassociated with the measure value from the load cell 259.

In various embodiments, the electric brake control unit 250 may send thescale factor(s) to a database (e.g., memory 116) to be used for allfuture force measurements by the load cell 259 until the process 300 isrepeated.

Referring now to FIG. 4 , a process 400 for health management of a loadcell 259 of an electric brake actuator 219 is illustrated, in accordancewith various embodiments. The process 400 may be performed by theelectric brake control unit 250. The present disclosure is not limitedin this regard.

The process 400 comprises determining a set of scale factors for a loadcell 259 based on calibrating the load cell 259 (step 402). In variousembodiments, the set of scale factors may be determined by the process300 from FIG. 3 as described previously herein.

The process 400 further comprises storing (e.g., in the memory 116 ofthe electric brake control unit 250) any scale factors that exceed ascale factor threshold as the scale factor threshold (step 404). Forexample, a scale factor threshold for each load cell 259 may be set,such as 20%, 25%, or the like. In this regard, any scale factor greaterthan the scale factor threshold (e.g., 1.2 for a 20% threshold) would bereduced to the scale factor threshold (e.g., a measured scale factor of1.3 would be reduced to 1.2 for storing in the memory 116 of theelectric brake control unit 250 for a 20% threshold), in accordance withvarious embodiments.

The process 400 further comprises counting a number of times the scalefactor threshold is applied (step 406). In this regard, every time ameasurement of the load cell 259 is based on a reduced scaled factordetermined from step 404, the electric brake control unit 250 may addone to the number of times the scale factor threshold has been applied.In this regard, step 406 continues counting each time the reduced scalefactor determined from step 404 is applied until a count threshold isexceed (e.g., as in step 408 as described further herein), or until theload cell 259 is recalibrated by process 300 and the scale factor nolonger exceeds the scale factor threshold. In this regard, in responseto the scale factor returning to acceptable ranges (e.g., below thescale factor threshold), the count may be reset, in accordance withvarious embodiments.

The process 400 further comprises generating a notification in responseto the number of times the scale factor threshold is applied to the loadcell measurement of the load cell 259 exceeds a count threshold (step408). In this regard, the electric brake control unit 250 may send asignal to a cockpit of the aircraft indicating the electric brakeactuator 219 of the respective load cell 259 that the electric brakeactuator 219 should be serviced.

The process 400 may further comprise servicing the electric brakeactuator (step 410).

In various embodiments, instead of counting a number of times a scalefactor threshold is used instead of a calculated scale factor todetermining servicing of the electric brake actuator 219, a thresholdscale factor rate of change, a threshold standard deviation for thescale factors, or the like may be utilized. In this regard, one skilledin the art may recognize various criteria that may be utilized todetermine a load cell 259 should be replaced and be within the scope ofthis disclosure.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosure. The scope of the disclosure is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”Moreover, where a phrase similar to “at least one of A, B, or C” is usedin the claims, it is intended that the phrase be interpreted to meanthat A alone may be present in an embodiment, B alone may be present inan embodiment, C alone may be present in an embodiment, or that anycombination of the elements A, B and C may be present in a singleembodiment; for example, A and B, A and C, B and C, or A and B and C.Different cross-hatching is used throughout the figures to denotedifferent parts but not necessarily to denote the same or differentmaterials.

In various embodiments, processes 300, 400 provide load cell driftcompensation and health monitoring for electric brake actuators forbraking system 200. In various embodiments, the processes 300, 400provide enhanced performance over time benefits, advanced notice fordegraded load cells to be services, and/or provide greater schedulingcapabilities for operators to perform maintenance/servicing of electricbrake actuators.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment,” “an embodiment,”“various embodiments,” etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Numbers, percentages, or other values stated herein are intended toinclude that value, and also other values that are about orapproximately equal to the stated value, as would be appreciated by oneof ordinary skill in the art encompassed by various embodiments of thepresent disclosure. A stated value should therefore be interpretedbroadly enough to encompass values that are at least close enough to thestated value to perform a desired function or achieve a desired result.The stated values include at least the variation to be expected in asuitable industrial process, and may include values that are within 10%,within 5%, within 1%, within 0.1%, or within 0.01% of a stated value.Additionally, the terms “substantially,” “about” or “approximately” asused herein represent an amount close to the stated amount that stillperforms a desired function or achieves a desired result. For example,the term “substantially,” “about” or “approximately” may refer to anamount that is within 10% of, within 5% of, within 1% of, within 0.1%of, and within 0.01% of a stated amount or value.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112(f) unless the element is expressly recitedusing the phrase “means for.” As used herein, the terms “comprises,”“comprising,” or any other variation thereof, are intended to cover anon-exclusive inclusion, such that a process, method, article, orapparatus that comprises a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus.

Finally, it should be understood that any of the above describedconcepts can be used alone or in combination with any or all of theother above described concepts. Although various embodiments have beendisclosed and described, one of ordinary skill in this art wouldrecognize that certain modifications would come within the scope of thisdisclosure. Accordingly, the description is not intended to beexhaustive or to limit the principles described or illustrated herein toany precise form. Many modifications and variations are possible inlight of the above teaching.

What is claimed is:
 1. A braking system for an aircraft, comprising: abrake assembly; a hydraulic braking subsystem having a hydraulic brakeactuator configured to operate the brake assembly; an electric brakingsubsystem having an electric brake actuator configured to operate thebrake assembly and a load cell configured to measure a force supplied bythe electric brake actuator; a hydraulic brake control unit configuredto control the hydraulic braking subsystem; and an electric brakecontrol unit configured to control the electric braking subsystem, theelectric brake control unit in operable communication with the hydraulicbrake control unit, wherein the electric brake control unit isconfigured to calibrate the load cell by a scale factor based on ameasured force from the load cell, a measured hydraulic pressure used toexceed the measured force received from the hydraulic brake controlunit, and a piston area of the hydraulic brake actuator.
 2. The brakingsystem of claim 1, wherein the electric brake control unit is furtherconfigured to store any scale factors that exceed a scale factorthreshold as the scale factor threshold.
 3. The braking system of claim2, wherein the electric brake control unit is further configured tocount a number of times the scale factor threshold is applied to a forcemeasurement of the load cell.
 4. The braking system of claim 3, whereinthe electric brake control unit is further configured to generate anotification in response to the number of times exceeding a countthreshold.
 5. The braking system of claim 1, wherein: the electric brakecontrol unit is further configured to command the electric brakeactuator to supply a first force to a brake stack of the brake assembly;and the hydraulic brake control unit is further configured to commandthe hydraulic braking subsystem to increase a supplied pressure to thebrake stack via the hydraulic brake actuator at a predetermined rate todetermine the hydraulic pressure used to exceed the measured force. 6.The braking system of claim 5, wherein the electric brake control unitis further configured to determine the hydraulic pressure from used toexceed the measured force based on the measured force dropping from aninitial measured force and pressure data received from the hydraulicbrake control unit.
 7. The braking system of claim 1, wherein theelectric brake control unit is further configured to determine a set ofscale factors including the scale factor, each scale factor in the setof scale factors associated with a commanded force for the electricbrake actuator.
 8. The braking system of claim 7, wherein a scale factoris interpolated in response to a second commanded force being between afirst commanded force having a first scale factor and the secondcommanded force having a second scale factor.
 9. The braking system ofclaim 1, wherein the electric brake control unit is further configuredto monitor a health of the load cell.
 10. The braking system of claim 1,wherein the electric brake control unit is configured to calibrate theload cell at a predetermined time interval.
 11. An article ofmanufacture including a tangible, non-transitory computer-readablestorage medium having instructions stored thereon that, in response toexecution by a processor, cause the processor to perform operationscomprising: commanding, via the processor, an electric brake actuator ofan electric braking subsystem of a braking system to supply a firstforce to a brake stack in the braking system; receiving, via theprocessor and from a hydraulic brake control unit, a pressure datacorresponding to a supplied pressure to the brake stack via a hydraulicbrake actuator at a predetermined rate; determining, via the processorand based on the pressure data, a pressure that causes a forcemeasurement of a load cell of the electric braking subsystem of thebraking system to drop; and calibrating, via the processor, the loadcell based on the pressure, the force measurement, and a piston contactarea of the electric brake actuator.
 12. The article of manufacture ofclaim 11, wherein the operations further comprise calculating a forcebased on the pressure and the piston contact area prior to calibrating.13. The article of manufacture of claim 11, wherein calibrating the loadcell comprises determining a scale factor for force measurement of theload cell that correlated with a commanded force of the electric brakeactuator.
 14. The article of manufacture of claim 13, wherein theoperations further comprise determining a set of scale factors, eachscale factor in the set of scale factors associated with the commandedforce of the electric brake actuator.
 15. The article of manufacture ofclaim 14, wherein the set of scale factors are associated with a ratioof the commanded force to a max rated force within a range of ratios.16. The article of manufacture of claim 15, wherein the range of ratiosis between 10% and 90% of the max rated force for the electric brakeactuator.
 17. An article of manufacture including a tangible,non-transitory computer-readable storage medium having instructionsstored thereon that, in response to execution by a processor, cause theprocessor to perform operations comprising: determining, via theprocessor, a set of scale factors for a load cell of an electric brakingsubsystem of a braking system, each scale factor in the set of scalefactors associated with a commanded force of an electric brake actuator;storing any scale factors that exceed a scale factor threshold as beingthe scale factor threshold; counting a number of times the load cell isscaled using the scale factor threshold as the scale factor; andgenerating a notification in response to the number of times exceeding acount threshold.
 18. The article of manufacture of claim 17, wherein theoperations further comprise re-calibrating, via the processor, the loadcell of the electric braking subsystem.
 19. The article of manufactureof claim 18, wherein the operations further comprise re-setting, via theprocessor, the counting to zero in response to the scale factor thatexceeded the scale factor threshold dropping below the scale factorthreshold.
 20. The article of manufacture of claim 17, whereindetermining the set of scale factors comprises calculating a scalefactor for a measured force of the load cell at the commanded force ofthe electric brake actuator to a brake stack based on a suppliedhydraulic pressure that forces a hydraulic brake actuator to reduce themeasured force on the brake stack.